Fig. 1.

Experimental setup. Bottom: participants squeezed a force transducer to move a cursor (triangles) to track a circular target. Vertical positions of the cursor and target on the display were proportional to the participant’s grip force and the target force level, respectively. Target changed colors from red to green whenever the cursor was inside a window around the target (this window was not visible). Top: on each trial, 96 total, the target remained fixed at 1 force level, and the trial waited until the cursor was inside the target window (shaded regions) for a contiguous 0.3 s before a 1.5-s block of grip force data was recorded (the beginning of the block is defined as trial time t = 0 s, the recording continuing even if the cursor left the window). During this block, 1 of 2 feedback conditions was applied. During control trials, the cursor continued to display the participant’s grip force (veridical feedback), although with a short delay due to filtering. During error-clamp trials, however, the average position of the cursor was locked on the target regardless of the participant’s grip force, giving the appearance of 0 error (i.e., nonveridical feedback). After this 1.5-s block, the target moved to a new position and a new trial began. MVC, maximum voluntary contraction.